Many computers (server apparatuses etc.) have conventionally been installed in for example a data center, a server room of a company, etc. Server apparatuses etc. are heat-producing objects during their operation. In a server room etc., heat produced by many server apparatuses etc. increase the ambient temperature, leading to a possibility that the increased temperature causes the server apparatuses etc. to fail. Accordingly, a cooling target space such as a server room etc. is provided with an air-conditioning system that keeps a constant temperature in the entire room. Air-conditioning systems such as this basically operate throughout the year, including winter.
An air-conditioning system such as this causes return air from for example a cooling target space to flow into the air-conditioning device so as to cool the return air in the air-conditioning device so that it becomes cold air, and supplies this cold air to the cooling target space. A rack group for example is installed in the cooling target space, and server apparatuses etc. are set in the respective racks. Each server apparatus is provided with a compact fan so that the cold air is inhaled into the server apparatus by the compact fan in order to cool the server apparatus.
The cold air is heated while it cools the server apparatuses, and becomes warm air. This warm air is discharged from the server apparatuses etc. or the racks and is discharged from the server room etc. as the above return air. The return air discharged from the server room etc. is cooled by the air-conditioning device to become cool air again, and is supplied to the server room etc. Alternatively, there is a configuration in which return air is discharged as exhausted air to the outside.
There is conventional technology disclosed by for example Patent Documents 1 and 2, etc. for the above air-conditioning system for a server room etc.
For example, there is conventional technology that uses a rack, for accommodating a server apparatus, including a front plane for inhaling cold air and an upper or rear plane for discharging return air in order to provide a recirculation preventive device for preventing the return air from recirculating to the front plane (Patent Document 1 for example). The conventional technology disclosed by Patent Document 1 can fix a closure shield to the upper plane of the rack so as to prevent the returned air from mixing with the cold air so that the cold air can be used effectively.
There is also conventional technology that includes a differential pressure sensor for measuring the differential pressure between the cold area and the hot area, controls an air blower on the basis of the measured value of this differential sensor, and thereby keeps the pressure in the cold area always higher than the pressure in the hot area (Patent Document 2 for example). Thereby, return air is prevented from recirculating to the cold area.    Patent document 1: Japanese Laid-open Patent Publication No. 2005-260148    Patent document 2: Japanese Laid-open Patent Publication No. 2011-242008